United States Patent (19) 11 Patent Number: 4,737,317 Wilson (45) Date of Patent: Apr. 12, 1988 54 PROCESS FOR PREPARING PHENYLDICHLOROPHOSPHINE OTHER PUBLICATIONS Kosolapoff, G. M. et al., Organic Phosphorus Com 75 Inventor: Glenn R. Wilson, Altamount, Ill. pounds, (1973), vol. 4, pp. 79-82, (Wiley-Interscience, 73 Assignee: Monsanto Company, St. Louis, Mo. Publ.). CRC Handbook of Chemistry and Physics, (1979-1980 (21) Appl. No.: 566,016 Ed.), CRC Press, Publ., pp. B-105 and C-146. (22 Filed: Dec. 27, 1983 Organic Syntheses, Coll., vol. 4, 784-785, (1963). 51) Int. Cl." ...... C07F 9/52 Primary Examiner-Donald B. Moyer 52 U.S. Cl...... 260/543 P Assistant Examiner-L. Hendriksen 58) Field of Search ...... 260/543 P Attorney, Agent, or Firm-Wendell W. Brooks; Arthur (56) References Cited E. Hoffman; Arnold H. Cole U.S. PATENT DOCUMENTS (57) ABSTRACT 3,029,282 4/1962 Toy et al...... 260/543 Phenyldichlorophosphine is prepared by contacting 3,057,917 10/1962 Maier ...... 260/543 benzene with phosphorus trichloride in the vapor phase 3,210,418 10/1965 Planfetti ...... 260/543 at a temperature from about 100° C. to about 145 C. in 3,864,394 2/1975 Via et al...... 260/543 P the presence of a catalyst consisting essentially of alumi 3,954,859 5/1976 Jurewicz et al...... 260/543 P nun metal and an activating amount of aluminum chlo ride. FOREIGN PATENT DOCUMENTS 443354 2/1969 Japan. 9 Claims, No Drawings 4,737,317 1. 2 benzene, phosphorus trichloride, and aluminum chlo PROCESS FOR PREPARING ride at reflux temperatures, and treating the resulting PHENYLDICHLOROPHOSPHINE hot reaction mixture with phosphorus oxychloride. Although these prior art processes generally provide BACKGROUND OF THE DISCLOSURE 5 the desired product, they nevertheless are limited in 1. Field of the Invention their application. Principal among these limitations, are This invention relates to a process for the preparation the drastic and severe reaction conditions which must of phenyldichlorophosphine. More particularly, this be employed which leads to the substantial production invention relates to a process for the vapor phase prepa of decomposition products. The discovery of the rela ration of phenyldichlorophosphine at temperatures 10 tively low temperature, vapor phase process of the from about 100° C. to about 145 C. in the presence of present invention is therefore believed to be a decided a catalyst consisting essentially of aluminum metal and advance in the state of the art. an activating amount of aluminum chloride. Phenyldichlorophosphine is a very useful intermedi SUMMARY OF THE INVENTION ate compound in organic synthesis. It may be used to 15 This invention is directed to a process for the vapor prepare various phosphorus-containing insecticides and phase reaction of benzene and phosphorus trichloride at to prepare the corresponding phosphonous acid, temperatures from about 100° C. to about 145 C. in the C6H6P(OH)2. Extensive quantities of phenyldichloro presence of a catalyst consisting essentially of aluminum phosphine are used each year for these purposes. metal and an activating amount of aluminum chloride. 2. Description of the Prior Art 20 Accordingly, typical objects of this invention are to Various processes for the preparation of aryldihalo provide a relatively low-temperature vapor phase pro phosphines are known in the art. The preparation of cess for the preparation of phenyldichlorophosphine aryldichlorophosphine, inter alia, is described in U.S. and to provide a vapor phase process for preparing Pat. No. 3,954,859. In this process, an aromatic hydro phenyldichlorophosphine at temperatures from about carbon selected from benzene, toluene, and xylene is 25 100 C. to about 145 C. characterized by high reactant reacted with phosphorus trichloride in the presence of a conversions and high phenyldichlorophosphine selec crystalline aluminosilicate zeolite in the hydrogen form tivity. catalyst at a temperature from 147 to 475 C. In this reaction, benzene and phosphorus trichloride yield phe These and other objects, aspects, and advantages of nyldichlorophosphine. 30 the invention, which will become apparent to those In U.S. Pat. No. 3,864,394 is described a process skilled in the art from the accompanying description wherein phenyldichlorophosphine (phenylphospho and claims are achieved by the process disclosed herein nous dichloride) is prepared by reacting chlorobenzene, for the preparation of phenyldichlorophosphine which phosphorus trichloride, and elemental phosphorus in an comprises contacting benzene with phosphorus trichlo autoclave at a temperature from about 275 C. to about 35 ride in the vapor phase at a temperature from about 100' 400 C. for a period of time from about 0.25 hour to C. to about 145 C. in the presence of a catalyst consist about 30 hours. ing essentially of aluminum metal and an activating U.S. Pat. No. 3,210,418 discloses the preparation of amount of anhydrous aluminum chloride. phenyldichlorophosphine by reacting benzene with DESCRIPTION OF THE PREFERRED phosphorus trichloride at a temperature of 725 C. in 40 the presence of a homogeneous gaseous catalyst, for EMBODIMENTS example, molecular oxygen, halogens, or nitrogen ox In accordance with this invention, phenyldichloro ides, which function as a free radical promoter. phosphine (also known as phenylphosphonous dichlo In U.S. Pat. No. 3,057,917 is described a process for ride) is prepared by a vapor phase process which com preparing, inter alia, arylhalophosphines which com 45 prises contacting benzene with phosphorus trichloride prises reacting an aryl halide, in the vapor phase, with in the vapor phase at a temperature from about 100 C. red phosphorus in the presence or absence of a metal to about 145 C. in the presence of a catalyst consisting catalyst selected from the group consisting of copper, essentially of aluminum metal and an activating amount nickel, silver, tin, antimony, and alloys of copper with at of aluminum chloride. The process is characterized by least one other metal of the group of metals. The aryl 50 high reactant conversion and high phenyldichlorophos dihalophosphine reportedly is the predominant species. phine selectivity. U.S. Pat. No. 3,029,282 describes a process for the The catalyst essential for use in the present invention preparation of phenyldichlorophosphine wherein ben consists essentially of aluminum metal and an activating Zene and phosphorus trichloride are reacted attempera amount of aluminum chloride. The aluminum metal can tures of at least 350° C. in the presence of chloroben 55 exist in any convenient form which can provide the zene. The presence of chlorobenzene reportedly in necessary surface to catalyze the desired reaction be creases the reaction rate, decreases decomposition tween the benzene and the phosphorus trichloride to products, and improves the quality of the phenyldi yield phenyldichlorophosphine. Suitable forms for the chlorophosphine. aluminum metal include aluminum wire (conveniently In Japanese Pat. No. Sho 44(1969-3354 a process for 60 shaped into a coil) and particulate aluminum metal. In the preparation of phenyldichlorophosphine is de general, aluminum wire is preferred. scribed whereinbenzene and phosphorus trichloride are The amount of aluminum metal employed in the in reacted at a temperature of 550° C. to 850 C. in the stant process is not narrowly critical. All that is neces presence of carbon tetrachloride. sary is that the aluminum metal is employed in an Finally, in an article in Organic Syntheses, Coll. Vol. 4, 65 amount sufficient to catalyze the reaction between the 784-785 (1963), there is disclosed a process for the prep benzene and phosphorus trichloride. Although larger or aration of phenyldichlorophosphine which comprises smaller amounts can be employed, if desired, an amount reacting in the liquid phase a homogeneous solution of of aluminum from about 0.10 mole to about 1.0 mole per 4,737,317 3 4 mole of phosphorus trichloride is generally sufficient, num chloride) contained in a suitable vessel. Similarly, with about 0.40 mole to about 0.70 mole being pre in a continuous operation, the vaporized reactant may ferred. be contacted in the presence of a moving or ebullient In addition to the aluminum metal, the catalyst also bed of (particulate) catalyst. includes a catalyst activating amount of aluminum chlo Following the reaction of the benzene with the phos ride. The actual amount of aluminum chloride em phorus trichloride, the reaction mixture is treated for ployed is not critical. All that is necessary is that an the recovery of, or the gas chromatographic analysis amount sufficient to activate the catalyst and initiate for, the phenyldichlorophosphine product. The reac reaction between the benzene and phosphorus trichlo tion mixture is cooled and diluted with benzene. To the ride is present. A trace amount, for example, 0.000010 to O resultant mixture is added a calculated amount of p 0.0010 gram per gram of aluminum metal, is usually dioxane (calculated from the weight loss of the alumi sufficient although, if desired, both larger and smaller nun metal catalyst) to decompose the aluminum-con amounts may be employed. taining phenyldichlorophosphine complex. The freed As previously noted, contact of the benzene with the phenyldichlorophosphine product is then analyzed by phosphorus trichloride in the presence of the catalyst is 15 gas chromatography or purified, if desired, by conven effected in the vapor phase. The benzene and phospho tional means, for example, vacuum distillation. rus trichloride are heated to the vaporization tempera It will be noted that, in addition to the aluminum-con ture at atmosphereic pressures and the vaporous mix taining phenylidichlorophosphine complex, an unidenti ture is brought into contact with the catalyst which is fied aluminum-containing complex, assumed to be an located in a reaction zone previously heated to the de 20 aluminum-containing complex of diphenylchlorophos sired reaction initiation temperature. Suitable reaction phine (from benzene and phenyldichlorophosphine), is initiation temperatures (and actual reaction tempera also present in the reaction mixture. Apparently, the tures) range from about 100° C. to about 145 C. organic ligand is bound more tightly to the aluminum in Once the reaction is initiated, the heat of reaction the latter complex in that p-dioxane fails to induce the from the exothermic reaction is sufficient to maintain 25 desired decomposition to permit easy and reliable analy the reaction at a temperature of about 115-5 C. with sis of such species by gas chromatography or purifica out the application of additional heat to the reaction tion by conventional means. zone. However, if a higher reaction temperature, for The following specific examples illustrating the best example, in excess of about 120 C. up to about 145 C., known methods of practicing this invention are de is desired, additional heat must be supplied to the reac 30 scribed in detail in order to facilitate a clear understand tion zone to maintain such higher temperature. In gen ing of the invention. It should be understood, however, eral, and as a practical matter, initiation of the reaction that the detailed expositions of the application of the at about 100 C. and maintenance of the reaction tem invention while indicating preferred embodiments, are perature at about 115-5 C. are preferred in that less given by way of illustration only and are not to be con energy is required to carry out the reaction. 35 strued as limiting the invention since various changes The process of this invention is conducted under and modifications within the spirit of the invention will substantially anhydrous conditions under an inert atmo become apparent to those skilled in the art from this sphere, for example, nitrogen, helium, argon, and the detailed description. like, with nitrogen generally being preferred for practi EXAMPLE 1. cal reasons. The carrying out of the reaction under 40 substantially anhydrous conditions is necessary in order A quartz tube arranged vertically and having a to avoid the ready hydrolysis of the phosphorus trichlo closed-loop sidearm fitted with a ground glass stop ride reactant. As employed herein, the term "substan pered opening in the upper portion for insertion and tially anhydrous' means not more than one weight removal of catalyst, a Nichrome wire heating coil for percent water is present in the reaction. 45 supplying heat, and a thermometer-containing thermo The reaction of benzene with phosphorus trichloride well for temperature measurements in the reaction to form phenyldichlorophosphine involves reaction of zone, and a dip tube extending from a point above the one mole of benzene with one mole of phosphorus tri lower sidearm loop to a point below the liquid level in chloride. Accordingly, the reaction may be carried out the benzene-phosphorus trichloride vaporization flask employing one mole of benzene for each mole of phos 50 (described below) was employed as the reactor. The phorus trichloride. However, it is preferred to employ a tube was fitted at the lower end with a suitably-sized molar excess of benzene over the phosphorus trichlo round bottom flask equipped with a thermometer-con ride. A suitable mole ratio of benzene to phosphorus taining thermowell for temperature measurements for trichloride for carrying out the reaction, therefore, vaporizing the benzene and phosphorus trichloride re ranges from about 1.0 to to about 10.0 or higher, with 55 actants and at the upper end with a water-cooled reflux mole ratios from about 3.0 to about 5.0 being preferred. condenser. The reflux condenser was equipped with a The present process may be conducted as a batch three-way stopcock valve as an inlet for nitrogen and as operation or a continuous operation. In carrying out the an outlet for hydrogen chloride (HCl) evolved during reaction as a batch operation, the vaporized reactants the course of the reaction. The outlet was fitted in series are contacted in the presence of the catalyst in a suitable 60 with a dry ice-acetone cold trap and an HCl gas scrub reaction vessel for a term sufficient to effect a desired ber. extent of reaction. This required time is not critical and Aluminum wire 0.16 cm (0.0625 in) diameter, 8.64 g, can range from about two hours to about 10 hours, with 0.320 g-atom was wound into a coil and fitted into the about five hours to about eight hours being sufficient. sidearm of the reaction system. The vaporization flask The reaction, however, may be carried out as a continu 65 was charged with 46.00 g (0.589 mole) of benzene, 77.50 ous operation. In continuous operations, the vaporized g (0.564 mole) of phosphorus trichloride (PCl3), and a reactant can be passed through a bed of the catalyst few boiling chips and attached to the quartz tube reac (aluminum metal plus an activating amount of alumi tor. The system was flushed with the nitrogen and a 4,737,317 5 6 trace of aluminum chloride (AlCl3) sprinkled onto the aspirator vacuum. The viscous concentrate was diluted aluminum wire coil. The sidearm was heated to 99-105 with 30 ml of benzene (immiscible) and 19.27 g (0.219 C. and the benzene-PCl3 mixture heated to reflux to mole) of p-dioxane added. The crystalline precipitate drive the vaporous mixture into the heated sidearm to was filtered off (under nitrogen) through a Celite filter contact the catalyst contained therein. Droplets of 5 bed and the precipitate washed with benzene, which brown-colored oil formed almost immediately on the was added to the filtrate (completely miscible). Gas aluminum wire and flowed down into the vaporization chromatographic analysis of the filtrate indicated it to flask and evolution of HCl commenced. At this point contain 0.146 mole of C6H5PCl2. The total isolable the reaction became exothermic and application of heat yield of C6H5PCl2 was 0.146 mole, 35.3% of theory to the sidearm was discontinued. The temperature in the 10 based upon the conversion of PCl3 as determined by the sidearm maintained itself at 1155 C. throughout the moles of HCl evolved. Separation and purification of reaction period. After 7.8 hours, a total of 0.389 mole of the product mixture may be carried out by concentra HCl had evolved. The reaction mixture in the flask, a tion and vacuum distillation as noted in Example 1 dark brown-colored viscous oil, was cooled to ambient above. The amount of aluminum consumed was 5.88 g temperatures and diluted (incompletely miscible) with 15 (0.218 g-atom). 60 ml of benzene. To the benzene-diluted reaction mix Thus, it is apparent that there has been provided, in ture was added 21.6 g (0.245 mole) of p-dioxane accordance with the present invention, a process that (amount calculated from the amount of aluminum wire fully satisfies the objects and advantages set forth here consumed as determined below) with stirring. A crys inabove. While the invention has been described with talline precipitate formed and the mixture was heated to respect to various specific examples and embodiments 70° C., cooled to ambient temperatures, and filtered thereof, it is understood that the invention is not limited (under nitrogen) through a Celite filter bed. The filtrate thereto and that many alternatives, modifications, and was a clear, red-colored liquid. The precipitate (as variations will be apparent to those skilled in the art in sumed to be a p-dioxane-AlCl3 complex) was washed light of the foregoing description. Accordingly, it is with benzene and the washings added to the filtrate 25 which then separated into two phases. The two phases intended to embrace all such alternatives, modifications, were separated and analyzed by gas chromatography and variations as fall within the spirit and broad scope individually. The upper layer was found to contain of the invention. 0.027 mole of phenyldichlorophosphine (C6H5PCl2), What is claimed is: while the lower layer contained 0.077 mole of 30 1. A process for the preparation of phenyldichloro C6HsPCl2. The total isolable yield of C6H5PC12 was phosphine which comprises contacting benzene with 0.104 mole, 26.7% of theory based upon the conversion phosphorous trichloride in the vapor phase at a temper of PCl3 as determined by the amount of HCl evolved ature from about 100° C. to about 145 C. in the pres (0.389 mole). Concentration and vacuum distillation of ence of a catalyst consisting essentially of aluminum the phenyldichlorophosphine product mixture may be 35 metal in an amount sufficient to provide from about 0.40 carried out to yield pure product: C6H5PCl2 bp mole to about 0.70 mole per mole of phosphorus trichlo 140-142 C. (57 mm Hg, 7.60 kPa), Kosolapoff, Organo ride and a catalyst activating amount of aluminum chlo phosphorus Compounds, John Wiley & Sons, Inc., New ride in an amount sufficient to provide from about York, 1950, p. 54. 0.000010 to about 0.0010 gram per gram of aluminum The aluminum wire was removed from the reactor metal. sidearm, cleaned with acetone, and weighed. The 2. The process of claim 1 wherein the aluminum weight loss, which corresponds to the amount of alumi metal is a coil of aluminum wire. num consumed, was 6.58 g (0.244 g-atom). This quan 3. The process of claim 1 wherein the benzene/phos tity was used to calculate the amount of p-dioxane re phorus trichloride mole ratio is from about 1.0 to about quired to decompose the aluminum-containing 45 10.0. C6H5PCl2 complex, assuming a 1/1 mole ratio. 4. The process of claim 3 wherein the benzene/phos phorus trichloride mole ratio is from about 3.0 to about EXAMPLE 2 5.0. The reaction system described in Example 1 above 5. The process of claim 1 wherein the benzene/phos was employed. An aluminum wire coil (8.66 g, 0.320 50 phorus trichloride reaction is initiated at a temperature g-atom) was fitted into the sidearm of the system and of about 100 C. the vaporization flask was charged with 46.24 g (0.592. 6. The process of claim 1 wherein the reaction tem mole) of benzene and 78.39 g (0.470 mole) of PCl3. The perature is maintained at about 115-5 C. system was flushed with nitrogen and a trace of AlCl3 7. The process of claim 6 wherein the reaction tem sprinkled onto the aluminum wire. The sidearm was 55 perature is maintained by the heat of reaction. heated to 134 C. and the benzene-PCl3 mixture heated 8. The process of claim 1 wherein the reaction tem to reflux to drive the vaporous mixture into the heated perature is maintained at a temperature in excess of sidearm to contact the catalyst contained therein. The about 120° C. up to about 145° C. temperature in the sidearm was maintained at 130-5 9. The process of claim 8 wherein the reaction tem by applying external heat. After 8.3 hours a total of 60 perature is maintained by the addition of heat to the 0.414 mole of HCl had evolved. The reaction mixture reaction Zone. was stripped of unreacted benzene and PCl3 using water k k xk k k

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